A rigid foamed synthetic resin (such as a rigid polyurethane foam which may be hereinafter referred to also as “a rigid foam”) produced by reacting a polyol component with a polyisocyanate component in the presence of a blowing agent, etc., is widely used as a heat-insulating material having closed cells.
As a blowing agent to be used for such a rigid foam, a hydrofluorocarbon compound or a hydrocarbon compound having a low boiling point is mainly used.
With respect to a rigid foam represented by e.g. a board-stock foam, further density reduction of the foam is desired in order to reduce the cost or the weight by reducing the amount of the raw material to be used. However, there is a problem such that along with density reduction of a foam, the strength of the foam tends to decrease, and the rigid foam is likely to undergo shrinkage.
Further, with respect to a blowing agent, in consideration of a load to the environment, it has been studied to reduce a low boiling point hydrofluorocarbon compound and increase water, or in consideration of the flammability, it has been studied to reduce a hydrocarbon compound and increase water, or a technique has been studied to use only water without using a low boiling point hydrofluorocarbon compound or hydrocarbon compound.
However, in a case where density reduction of a foam is attempted by combining water with a hydrofluorocarbon compound or hydrocarbon compound, or density reduction of a foam is attempted by water-foaming by carrying out foaming by means of only water, the foam tends to be remarkably susceptible to shrinkage, thus leading to deterioration in dimensional stability of the foam.
In order to secure the dimensional stability of a foam, it is usually conceivable to increase the density of the foam thereby to increase the strength of the foam, or to make cells of the foam to be open cells.
However, in the method of increasing the density of the foam, the amount of the raw material to be used increases, thus leading to an increase in cost. On the other hand, in the method of making cells of the foam to be open cells, no adequate heat-insulating properties can be obtained, although the dimensional stability of the foam may thereby be improved.
That is, a rigid foam is desired to have good dimensional stability and sufficient heat-insulating properties when water is used as a blowing agent in a large amount or when foaming is carried out solely by water.
Heretofore, a method of using a fluorinated compound such as polytetrafluoroethylene (PTFE) has been proposed as prior art to improve the dimensional stability by preventing shrinkage of a rigid polyurethane foam (Patent Documents 1 and 2). According to the method disclosed in Patent Documents 1 and 2, by addition of PTFE having a small particle size, fine pores may be formed in the foam, whereby the dimensional stability will be improved, and at the same time good heat-insulating properties can be obtained.
Further, a method of incorporating a polymer-dispersed polyol to a polyol component is proposed (Patent Documents 3 and 4).
Here, “the polymer-dispersed polyol” is a polyol having polymer particles dispersed in a polyol such as a polyether polyol or a polyester polyol.
Such a polymer-dispersed polyol has heretofore been used to improve the hardness of a flexible foam or semi-rigid foam.
As a typical example of the method for producing a polymer-dispersed polyol, the following method is known. That is, it is a method of carrying out polymerization of a monomer having a polymerizable unsaturated group in a saturated polyol having no polymerizable unsaturated bond, if required, under such a condition that an unsaturated polyol having a polymerizable unsaturated bond is also present, followed by removing an unreacted component. As such a saturated polyol or unsaturated polyol, various polyether polyols or polyester polyols are known.
Patent Document 1: EP0224945
Patent Document 2: JP-A-8-503720
Patent Document 3: JP-A-57-25313
Patent Document 4: JP-A-11-302340